In “Grudge Match,” Stallone and De Niro play Henry “Razor” Sharp and Billy “The Kid” McDonnen, two local Pittsburgh fighters whose fierce rivalry put them in the national spotlight.

Each had scored a victory against the other during their heyday, but in 1983, on the eve of their decisive third match, Razor suddenly announced his retirement, refusing to explain why but effectively delivering a knock-out punch to both their careers.

Thirty years later, boxing promoter Dante Slate Jr., seeing big dollar signs, makes them an offer they can’t refuse: to re-enter the ring and settle the score once and for all.

But they may not have to wait that long: on their first encounter in decades, their long-festering feud erupts into an unintentionally hilarious melee that instantly goes viral.

The sudden social media frenzy transforms their local grudge match into a must-see HBO event.

Now, if they can just survive the training, they may actually live to fight again.

The film also stars Kevin Hart (“Think Like a Man”) as Dante Slate Jr.; Oscar® winner Alan Arkin as Razor’s former trainer, Louis “Lightning” Conlon, who gets to put Razor through his paces again; and Oscar® winner Kim Basinger (“L.A. Confidential”) as Sally Rose, who was once the love of Razor’s life.

Rounding out the cast are Jon Bernthal (upcoming “The Wolf of Wall Street,” TV’s “The Walking Dead”) as BJ, who becomes The Kid’s instinctive but untested trainer; and young film newcomer Camden Gray (“Californication”).

Segal is directing from a screenplay by Rodney Rothman, story by Tim Kelleher. The film is being produced by Bill Gerber (“Gran Torino”), Mark Steven Johnson (“Grumpy Old Men,” “Grumpier Old Men”), Michael Ewing (“Get Smart”) and Ravi Mehta (“The Lucky One”). Peter Segal, Jane Rosenthal and Kevin King-Templeton are serving as executive producers.

Collaborating with Segal behind the scenes are: Academy Award®-winning cinematographer Dean Semler (“Dances With Wolves,” “Apocalypto”); production designer Wynn Thomas (“Cinderella Man”); costume designer Mary Vogt (“Men in Black 3”); and editor William Kerr (“Bridesmaids”). Robert Sale, who was the technical advisor on “Rocky Balboa,” is serving as the film’s boxing consultant. The music is by Trevor Rabin.